In the production process of electronic parts such as semiconductor ICs, etc., magnetron sputtering methods having high film-forming speeds by targets and capable of forming thin films at low temperatures because electrons are not impinged onto substrates are widely used to form thin films on substrates.
A phenomenon that atoms or molecules are ejected from a target by a high-speed bombardment of an inert substance such as Ar, etc. is called “sputtering.” The ejected atoms or molecules can be accumulated on a substrate to form a thin film. A magnetron sputtering method uses a magnetic field in a cathode to increase a film-forming speed, thereby improving the productivity.
A magnetron sputtering apparatus comprises a substrate (anode), a target (cathode) arranged to oppose the substrate, and a magnetic-field-generating apparatus arranged below the target, in a vacuum chamber. With voltage applied between the anode and the cathode to cause glow discharge for ionizing an inert gas (Ar at about 0.1 Pa, etc.) in the vacuum chamber, secondary electrons discharged from the target are captured by a magnetic field generated by the magnetic-field-generating apparatus, so that cyclotron motion occurs on a target surface. Because the cyclotron motion of electrons accelerates the ionization of gas molecules, a film-forming speed is dramatically higher than when a magnetic field is not used, resulting in strong adhesion of a film.
As shown in FIG. 29, a magnetic circuit apparatus 4 used in a magnetron sputtering apparatus comprises a center rod-shaped magnet 410 magnetized in a height direction (perpendicular to a target surface), a peripheral rectangular magnet 420 arranged around the center magnet 410 and magnetized in an opposite direction to the center magnet 410, and a yoke 430 supporting the center magnet 410 and the peripheral magnet 420, to generate a leaked magnetic field in a racetrack form in parallel to a target surface (for example, see JP 8-134640 A). With a racetrack-shaped magnetic circuit, secondary electrons can be contained in a closed space, resulting in a high secondary electron density and thus high sputtering efficiency. To form this closed space, a magnetic field of 10 mT or more in a horizontal component of a magnetic flux density is usually needed.
The erosion of a target is fastest in a portion shown by a broken line in FIG. 30, in which a perpendicular component of a magnetic flux density is zero, and by adjusting a magnetic field to cause uniform erosion in this portion, a target can be used for a long period. However, when plasma is contained on a target surface by a magnetic circuit apparatus 4 as shown in FIG. 29, plasma formed in the linear portion is concentrated in the corner portions, resulting in rapid erosion in the corner portions. The concentration of plasma occurs by a magnetic flux concentrated in the corner portions, because a portion in which a perpendicular component of a magnetic flux density is zero is located at a distance R from the center magnet 410 in the linear portion, and at a smaller distance r (r<R) in the corner portions.
JP 8-134640 A discloses a technology of arranging magnets having a smaller residual magnetic flux density in a T form in corner portions, to eliminate the unevenness of a perpendicular component of a magnetic flux density in the corner portions. However, its improvement is not sufficient, making it desirable to develop a technology of alleviating the concentration of a magnetic flux in the corner portions.
JP 2008-156735 A discloses, as shown in FIGS. 31(a) and 31(b), a magnetic-field-generating apparatus 5 for magnetron sputtering, which comprises a non-magnetic base 510, a rectangular center magnetic pole piece 520 disposed on a surface of the non-magnetic base 510, a peripheral racetrack-shaped magnetic pole piece 530 disposed around the rectangular center magnetic pole piece 520, and plural permanent magnets 540, 550 arranged between the center magnetic pole piece and the peripheral magnetic pole piece, the permanent magnets 540, 550 being magnetized in a horizontal direction (in parallel to a target surface) and arranged with their magnetic poles of the same polarity opposing the center magnetic pole piece, and the center magnetic pole piece and the peripheral magnetic pole piece being higher than the permanent magnets. JP 2008-156735 A describes that because magnetic pole surfaces of the permanent magnets are in contact with the magnetic pole pieces in this magnetic-field-generating apparatus, the leakage of magnetic flux from the permanent magnets is reduced, so that a predetermined magnetic flux can be generated by a smaller number of permanent magnets than in the above magnetic circuit apparatus comprising magnets magnetized in a height direction. JP 2008-156735 A further describes that a region providing a magnetic field intensity of 10 mT or more in a horizontal component of a magnetic flux density, which is necessary for containing an inert gas excited to a plasma state, is expanded than before, thereby expanding an erosion region of a target, providing uniform erosion between the linear portion and the corner portions, thereby forming a uniform-thickness film on a substrate.
However, because the magnetic-field-generating apparatus described in JP 2008-156735 A comprises a non-magnetic base, a magnetic field leaks on the opposite side of the target in the magnetic circuit, adversely affecting control equipments for the sputtering apparatus disposed on the opposite side of the target. When large magnetic field leakage occurs on the opposite side of the target, electronic devices cannot disadvantageously be arranged on a rear side of the magnetic circuit. Though a magnetic circuit base may be formed by a magnetic material such as iron to prevent magnetic field leakage, only a small amount of a magnetic field appears on the target side because most magnetic fields generated pass through the magnetic base. Further, because most part of the linear portion is occupied by magnets in the magnetic-field-generating apparatus described in JP 2008-156735 A, fastening members such as screws are not easily arranged there, making it difficult to fix it to a sputtering apparatus.
Thus desired is the development of an efficient magnetic-field-generating apparatus for magnetron sputtering, which has the reduced influence of a leaked magnetic field on a sputtering apparatus, is easily fixed to a sputtering apparatus, and provides the uniform erosion of a target.
As a technology of expanding an erosion region to provide a proper perpendicular component distribution of a magnetic field on a target surface in the use of a magnetic circuit apparatus 4 as shown in FIG. 29, JP 2006-16634 A discloses a magnetic-field-generating apparatus comprising magnetic plates (shunt plates) arranged in parallel to a target surface between the magnetic pole of the center magnet and the magnetic pole of the peripheral magnet. JP 2006-16634 A describes that the shunt plates contribute to the formation of a region in which a perpendicular component of a magnetic field generated by the magnetic circuit on a target surface is zero or flat near zero, or a region crossing the zero point three times.
However, because the magnetic-field-generating apparatus described in JP 2006-16634 A has a structure in which shunt plates are arranged between the magnetic circuit and the target, the removal and position adjustment of the shunt plates for adjusting a magnetic field cannot easily be conducted. Also, because vacuum should be released when a target-containing chamber is in a vacuum state, for example, a demand for adjusting a magnetic field depending on the erosion of a target during sputtering cannot be met.
In electronic parts constituted by multilayer thin films such as semiconductor ICs, etc., various metal films and alloy films are necessary, needing different targets for various layers. In a sputtering apparatus for producing such electronic parts, sputtering should be conducted with different targets for various layers under conditions suitable for them. Because magnetic field intensity is one of factors having large influence on production efficiency and the properties of metal films among sputtering conditions, there is a demand for properly adjusting magnetic field intensity for each of layers formed with different targets. Though the adjustment of magnetic field intensity is possible to some extent by changing the distance between the magnetic-field-generating apparatus and the target, it is extremely difficult to change a magnetic field finely depending on the position of the target. Thus, the development of a magnetic-field-adjusting means for an optimum magnetic circuit is desired.